Method for producing multilayered optical systems

ABSTRACT

Inorganic multilayered optical systems are produced by applying to a glass substrate a flowable composition containing nanoscale solid inorganic particles containing polymerizable or polycondensable organic surface groups, polymerizing and/or polycondensing those surface groups to form an organically crosslinked layer, applying to the organically crosslinked layer and polymerizing/polycondensing a flowable composition producing a different refractive index from the first layer (optionally repeated one or more times), and one-step thermal densifying and removing the organic components. The systems so produced are suitable as interference filters and antireflection systems.

BACKGROUND OF THE INVENTION

The invention relates to a method for producing multilayered opticalsystems by a one-step baking method (“stack baking”).

Multilayered systems having an optical effect can be produced on glassby the so-called sol-gel process; see, for example, Dislich et al. DE1941191. The principle of this production method is that thecorresponding glass substrate is coated with a sol by an immersionprocess, dried at elevated temperatures and baked in order to achievedensification. After pre-drying at temperatures of >100° C., it is alsopossible to apply a further layer by immersion and to bake the twolayers in one step. The pre-drying at elevated temperatures is necessaryin order to provide the first layer with adequate chemical stability,since it is otherwise partially or fully dissolved by the new coatingsol. The layer thickness which can be achieved with a plurality oflayers, without prior densification of each individual layer bysintering, is about 0.5 μm, since otherwise cracking occurs. Thecracking occurs as a consequence of the already strong three-dimensionalcrosslinking of the porous layer systems, since the shrinkage whichoccurs on heating can no longer be dissipated by stress relaxation. Inaddition, the method is also complex since heat treatment is necessaryafter each layer application and in the case of a plurality of layers,baking at temperatures of 400-500° C. becomes necessary. The productionof multilayered systems, as necessary in specific optical applications(broad-band antireflection coating, diathermic mirrors, etc.), becomesextremely labour-intensive and expensive.

Although it has been shown in WO 93/24424 that the incorporation ofrelaxation mechanisms enables thick layers to be produced as well, thesecannot, however, be used to achieve an optical effect since they do notsatisfy the condition of quarter-wave (λ/4) layers.

SUMMARY OF THE INVENTION

The object of the invention was to produce multilayered optical systemsas far as possible without complex intermediate heating steps in such away that the optical effect later desired occurs.

This object is achieved in accordance with the invention by a method forproducing multilayered optical systems which comprises the followingsteps:

a) application of a flowable composition comprising nanoscale inorganicsolid particles containing polymerizable and/or polycondensable organicsurface groups to a glass substrate;

b) polymerization and/or polycondensation of the surface groups of thesolid particles with formation of an organically crosslinked layer;

c) application to the organically crosslinked layer of a furthercomposition in accordance with a) which produces a different refractiveindex to the previous composition;

d) polymerization and/or polycondensation of the surface groups of thesolid particles with formation of a further organically crosslinkedlayer;

e) if desired, repetition of steps c) and d) one or more times withformation of further organically crosslinked layers on the organicallycrosslinked layers already present and/or on other surfaces of thesubstrate; and

f) one-step thermal densification of the multilayer system and removalof the organic constituents present by baking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the reflection spectrum of a glass sheet treated inaccordance with Example 5.

FIG. 2 shows the reflection spectrum of a glass sheet treated inaccordance with Example 6.

FIG. 3 shows the transmission spectrum of a glass sheet treated inaccordance with Example 7.

DETAILED DESCRIPTION OF THE INVENTION

The use of nanoscale particles coated with polymerizable and/orpolycondensable groups gives rise to the possibility of producingchemically stable layers even at very low temperatures, for example viaphotopolymerization, and in this way applying further layers by the samemethod. It has been found here, entirely surprisingly, that these layerscan be densified without cracking, even in the case of layer systemshaving up to 10 or more individual layers, and that their optical effectcan be calculated accurately in advance. This is given by the content ofinorganic components in the respective coating system, the amountapplied (layer thickness) and the refractive index achieved after finalthermal densification.

In the present description and the appended claims, the term “nanoscaleinorganic solid particles” is taken to mean particles having a meanparticle size (mean particle diameter) of not greater than 200 nm,preferably not greater than 100 nm, and in particular not greater than70 nm. A particularly preferred particle size range is from 5 to 50 nm.

The nanoscale inorganic solid particles can consist of any desiredmaterials, but preferably consist of metals and in particular of metalcompounds, such as, for example, “optionally hydrated” oxides, such asZnO, CdO, SiO₂, TiO₂, ZrO₂, CeO₂, SnO₂, Al₂O₃, In₂O₃, La₂O₃, Fe₂O₃,Cu₂O, Ta₂O₅, Nb₂O₅, V₂O₅, MoO₃ or WO₃; chalcogenides, such as, forexample, sulphides (for example CdS, ZnS, PbS and Ag₂S), selenides (forexample GaSe, CdSe and ZnSe) and tellurides (for example ZnTe or CdTe),halides, such as AgCl, AgBr, AgI, CuCl, CuBr, CdI₂ and PbI₂; carbides,such as CdC₂ or SiC; arsenides, such as AlAs, GaAs and GeAs;antimonides, such as InSb; nitrides, such as BN, AlN, Si₃N₄ and Ti₃N₄;phosphides, such as GaP, InP, Zn₃P₂ and Cd₃P₂; phosphates, silicates,zirconates, aluminates, stannates and corresponding mixed oxides (forexample those having a perovskite structure, such as BaTiO₃ and PbTiO₃)

The nanoscale inorganic solid particles employed in the method accordingto the invention are preferably those of oxides, sulphides, selenidesand tellurides of metals and mixtures thereof. In accordance with theinvention, particular preference is given to nanoscale particles ofSiO₂, TiO₂, ZrO₂, ZnO, Ta₂O₅, SnO₂ and Al₂O₃ (in all modifications, inparticular as boehmite, AlO(OH)) and mixtures thereof.

Since the nanoscale particles which can be employed in accordance withthe invention cover a broad range of refractive indices, the refractiveindex of the layer(s) can be set to the desired value in a comfortablemanner through a suitable selection of these nanoscale particles.

The nanoscale solid particles employed in accordance with the inventioncan be produced in a conventional manner, for example by flamepyrrolysis, plasma methods, gas-phase condensation methods, colloidtechniques, precipitation techniques, sol-gel processes, controllednucleation and growth processes, MOCVD methods and (micro)emulsionmethods. These methods are described in detail in the literature. Inparticular, it is possible to use, for example, metals (for exampleafter reduction in the precipitation method), ceramic oxidic systems (byprecipitation from solution), but also salt-like or multicomponentsystems. The salt-like or multicomponent systems also includesemiconductor systems.

The production of the nanoscale inorganic solid particles provided withpolymerizable and/or polycondensable organic surface groups which areemployed in accordance with the invention can be carried out by, inprinciple, two different methods, namely firstly by surface modificationof pre-produced nanoscale inorganic solid particles and secondly byproduction of these inorganic nanoscale solid particles using one ormore compounds which contain polymerizable and/or polycondensable groupsof this type. These two methods are described in greater detail belowand in the examples.

The organic polymerizable and/or polycondensable surface groups can beany desired groups known to the person skilled in the art which are ableto undergo free-radical, cationic or anionic, thermal or photochemicalpolymerization or thermal or photochemical polycondensation (ifnecessary in the presence of a suitable initiator or catalyst). Inaccordance with the invention, preference is given to surface groupswhich contain a (meth)acrylyl, allyl, vinyl or epoxide group, particularpreference being given to (meth)acrylyl and epoxide groups. In the caseof groups which are capable of undergoing polycondensation, mentionshould be made, in particular, of hydroxyl, carboxyl and amino groups,with the aid of which ether, ester and amide bonds between the nanoscaleparticles can be obtained.

It is also preferred in accordance with the invention for the organicgroups present on the surfaces of the nanoscale particles, which groupsinclude the polymerizable and/or polycondensable groups, to have arelatively low molecular weight. In particular, the molecular weight ofthe (purely organic) groups should not exceed 500 and preferably 300,particularly preferably 200. Of course, this does not exclude asignificantly higher molecular weight of the compounds (molecules)containing these groups (for example 1000 or more).

As already mentioned above, the polymerizable/polycondensable surfacegroups can in principle be provided by two methods. If surfacemodification of pre-produced nanoscale particles is carried out,suitable compounds for this purpose are all (preferablylow-molecular-weight) compounds which firstly have one or more groupswhich are able to react or at least interact with functional groups(such as, for example, OH groups in the case of oxides) present on thesurface of the nanoscale solid particles, and secondly have at least onepolymerizable/polycondensable group. Thus, the corresponding compoundscan, for example, form both covalent and ionic (salt-like) orcoordinative (complex) bonds to the surface of the nanoscale solidparticles, while pure interactions which may be mentioned by way ofexample are dipole-dipole interactions, hydrogen bridges and van derWaals interactions. Preference is given to the formation of covalentand/or coordinative bonds. Specific examples of organic compounds whichcan be used for the surface modification of the nanoscale inorganicsolid particles are, for example, unsaturated carboxylic acids, such asacrylic acid and methacrylic acid, β-dicarbonyl compounds (for exampleβ-diketones or β-carbonylcarboxylic acids) containing polymerizabledouble bonds, ethylenically unsaturated alcohols and amines, aminoacids, epoxides and the like. Compounds of this type which areparticularly preferred in accordance with the invention are—inparticular in the case of oxidic particles—hydrolytically condensablesilanes containing at least (and preferably) one non-hydrolyzableradical which contains a polymerizable carbon-carbon double bond or anepoxide ring. Silanes of this type preferably have the general formula(I):

X—R¹—SiR² ₃  (I)

in which X is CH₂═CR³—COO, CH₂═CH or glycidyloxy, R³ is hydrogen ormethyl, R¹ is a divalent hydrocarbon radical having 1 to 10, preferably1 to 6, carbon atoms which optionally contains one or more heteroatomgroups (for example O, S or NH) which separate adjacent carbon atomsfrom one another, and the radicals R², identical to or different fromone another, are selected from alkoxy, aryloxy, acyloxy andalkylcarbonyl groups and halogen atoms (in particular F, Cl and/or Br).

The groups R² are preferably identical and selected from halogen atoms,C₁₋₄-alkoxy groups (for example methoxy, ethoxy, n-propoxy, i-propoxyand butoxy), C₆₋₁₀ aryloxy groups (for example phenoxy), C₁₋₄-acyloxygroups (for example acetoxy and propionyloxy) and C₂₋₁₀-alkylcarbonylgroups (for example acetyl).

Particularly preferred radicals R² are C₁₋₄-alkoxy groups and inparticular methoxy and ethoxy.

The radical R¹ is preferably an alkylene group, in particular one having1 to 6 carbon atoms, such as, for example, ethylene, propylene, butyleneor hexylene. If X is CH₂═CH, R¹ is preferably methylene and can in thiscase also be a simple bond.

X is preferably CH₂═CR³—COO (in which R³ is preferably CH₃) orglycidyloxy. Accordingly, particularly preferred silanes of the generalformula (I) are (meth)-acryloyloxyalkyltrialkoxysilanes, such as, forexample, 3-methacryloyloxypropyltri(m)ethoxysilane, andglycidyloxyalkyltrialkoxysilanes, such as, for example,3-glycidyloxypropyltri(m)ethoxysilane.

If the nanoscale inorganic solid particles have already been producedusing one or more compounds which contain polymerizable/polycondensablegroups, subsequent surface modification can be omitted (although this isof course possible as an additional measure).

The in-situ production of nanoscale inorganic solid particles containingpolymerizable/polycondensable surface groups is explained below usingthe example of SiO₂ particles. For this purpose, the SiO₂ particles canbe produced, for example, by the sol-gel process using at least onehydrolytically polycondensable silane containing at least onepolymerizable/polycondensable group. Suitable silanes of this type are,for example, the silanes of the general formula (I) already describedabove. These silanes are preferably employed either alone or incombination with a suitable silane of the general formula (II)

 SiR² ₄  (II)

in which R² is as defined above. Preferred silanes of the above generalformula (II) are tetramethoxysilane and tetraethoxysilane.

It is of course also possible, in addition or as an alternative to thesilanes of the general formula (II), to employ other silanes, forexample those which contain a (non-hydrolyzable) hydrocarbon groupwithout any functional group, such as, for example, methyl- orphenyltrialkoxysilanes.

The composition employed in the process according to the invention is inthe form of a material which is still flowable (suspension). The liquidconstituent of this material is composed, for example, of water and/or(preferably water-miscible) organic solvents and/or compounds which wereemployed or formed during the production of the nanoscale particles ortheir surface modification (for example alcohols in the case ofalkoxysilanes). Any suitable organic solvents additionally employed are,for example, alcohols, ethers, ketones, esters, amides and the like.However, an (additional) constituent of the flowable material can alsobe, for example, at least one monomeric or oligomeric species whichcontains at least one group which is able to react (polymerize orpolycondense) with the polymerizable/polycondensable groups present atthe surface of the nanoscale particles. Examples of such species whichmay be mentioned are monomers containing a polymerizable double bond,such as, for example, acrylates, methacrylates, styrene, vinyl acetateand vinyl chloride. Preferred monomeric compounds containing more thanone polymerizable bond are, in particular, those of the general formula(III):

(CH₂═CR³—COZ—)_(n)—A  (III)

in which

n=2, 3 or 4, preferably 2 or 3, in particular 2;

Z=O or NH, preferably O;

R³=H or CH₃;

A an n-valent hydrocarbon radical having 2 to 30, in particular 2 to 20,carbon atoms, which may contain one or more heteroatom groups, eachlocated between two adjacent carbon atoms (examples of such heteroatomgroups are O, S, NH, NR (R=hydrocarbon radical), preferably O).

The hydrocarbon radical A may furthermore carry one or moresubstituents, which are preferably selected from halogen (in particularF, Cl and/or Br), alkoxy (in particular C₁₋₄-alkoxy), hydroxyl,optionally substituted amino, NO₂, OCOR⁵, COR⁵ (R⁵=C₁₋₆-alkyl orphenyl). However, the radical A is preferably unsubstituted orsubstituted by halogen and/or hydroxyl.

In one embodiment of the present invention, A is derived from analiphatic diol, an alkylene glycol, a polyalkylene glycol or anoptionally alkoxylated (for example ethoxylated) bisphenol (for examplebisphenol A).

Other suitable compounds containing more than one double bond are, forexample, allyl (meth)acrylate, divinylbenzene and diallyl phthalate. Itis likewise possible, for example, to use a compound containing two ormore epoxide groups (in the case of the use of epoxide-containingsurface groups), for example bisphenol A diglycidyl ether oralternatively an (oligomeric) precondensate of a hydrolyzable silanecontaining epoxide groups (for example glycidoxypropyltrimethoxysilane).

The proportion of organic components in the coating compositions used inaccordance with the invention is preferably not greater than 20 percentby weight, based on the solids content. It can be, for example, 5percent by weight for layers of high refractive index and, for example,15 percent by weight for layers of low refractive index.

The coating composition used in accordance with the invention preferablyhas a pH of ≧3, particularly preferably ≧4. In general, the pH is in theneutral region up to about 8, preferably up to about 7.5.

In step a) of the method according to the invention, the coatingcomposition is applied to a glass substrate in order to coat this fullyor partly. The coating methods which are suitable for this purpose arethe conventional methods known to the person skilled in the art.Examples thereof are dipping, spraying, knife coating, spreading,brushing or spin coating.

Before application to the substrate, the flowable material can be set toa suitable viscosity, for example by addition of solvent or evaporationof volatile constituents (in particular solvent already present).

Before application of the flowable material, the substrate can, ifnecessary, be subjected to pretreatment (for example cleaning,degreasing, etc.).

In step b) of the method according to the invention, a polymerizationand/or polycondensation of the polymerizable/polycondensable surfacegroups of the nanoscale inorganic solid particles (and, whereappropriate, the polymerizable/polycondensable groups of the monomericor oligomeric species additionally employed) is carried out. Thispolymerizable/polycondensation can be carried out in the manner which iscustomary to the person skilled in the art. Examples of suitable methodsare thermal, photochemical (for example using UV radiation), electronbeam curing, laser curing, room-temperature curing, etc. If necessary, apolymerization/polycondensation of this type is carried out in thepresence of a suitable catalyst or initiator, which is added to theflowable material at the latest immediately before application thereofto the substrate.

Suitable initiators/initiator systems are all conventionalinitiators/initiator systems which are known to the person skilled inthe art, including free-radical photoinitiators, free-radicalthermoinitiators, cationic photoinitiators, cationic thermoinitiatorsand any desired combinations thereof.

Specific examples of free-radical photoinitiators which can be employedare IRGACURE® 184 (1-hydroxycyclohexyl phenyl ketone), IRGACURE® 500(1-hydroxycyclohexyl phenyl ketone and benzophenone), and otherphotoinitiators sold under the IRGACURE® trademark by Ciba-Geigy,DAROCUR® 1173, 1116, 1398, 1174, and 1020 photoinitiators (obtainablefrom Merck); benzophenone, 2-chlorothioxanthone, 2-methylthioxanthone,2-isopropylthioxanthone, benzoin, 4,4′-dimethoxybenzoin, benzoin ethylether, benzoin isopropyl ether, benzil dimethyl ketal,1,1,1-trichloroacetophenone, diethoxyacetophenone and dibenzosuberone.

Examples of free-radical thermoinitiators are, inter alia, organicperoxides in the form of diacyl peroxides, peroxydicarbonates, alkylperesters, alkyl peroxides, perketals, ketone peroxides and alkylhydroperoxides, and also azo compounds. Specific examples which may bementioned here are, in particular, dibenzoyl peroxide, tert-butylperbenzoate and azobisisobutyronitrile.

An example of a cationic photoinitiator is CYRACURE® UVI-6974 (mixedtriarylsulfonium hexafluoroantimonate salts), while a preferred cationicthermal initiator is 1-methylimidazole.

These initiators are employed in the usual amounts known to the personskilled in the art (preferably 0.01-5% by weight, in particular 0.1-2%by weight, based on the total solids content of the coatingcomposition). It is of course also possible to omit the initiatorcompletely under certain circumstances, such as, for example, in thecase of electron beam or laser curing.

The polymerization/polycondensation in step b) of the method accordingto the invention is preferably carried out thermally or by irradiation(in particular using UV light). Particular preference is given tophotochemical polymerization/polycondensation or a combination ofthermal and photochemical polymerization/polycondensation.

Prior to the polymerization/polycondensation, further volatile,non-polymerizable/non-polycondensable compounds can be removed from thelayer applied to the substrate. This removal of volatile constituentscan, however, alternatively or additionally be carried out at thepolymerization/polycondensation stage or thereafter.

A typical method according to the invention will be outlined below byway of example, the stated value ranges and procedures having generalvalidity irrespective of the materials employed specifically.

Nanoscale particles of, for example, SiO₂, TiO₂, ZrO₂ or other oxidic orsulphidic materials (particle size from 30 to 100 nm, preferably from 40to 70 nm) are dispersed in a solvent (for example in a lower alcohol,such as methanol, ethanol or propanol) in a concentration of from 1 to20% by weight, preferably from 5 to 15% by weight, and a surfacemodifier containing polymerizable/polycondensable groups is added,preferably in an amount of from 2 to 25% by weight, in particular from 4to 15% by weight (based on the total solids content). In the case of theuse of silanes, for example, the surface modification can be carried outby stirring for several hours at room temperature. Subsequently, ifdesired, a monomeric or oligomeric material containingpolymerizable/polycondensable groups which is compatible with thesurface modifier or the surface groups can be added in an amount of, forexample, up to 20% by weight, preferably from 4 to 15% by weight (basedon the total solids content).

After adjustment of the viscosity by addition or removal of solvent, oneor more suitable initiators (in each case in an amount of, for example,from 0.01 to 5% by weight, based on the total solids content) and, ifdesired, other conventional additives are added.

The coating composition is then applied to the substrate, with theapplication rate generally being selected, depending on the desiredrefractive index and area of application, in such a way that layerthicknesses in the range from 50 to 200 nm, preferably from 100 to 150nm, are achieved.

The subsequent polymerization/polycondensation (cross-linking) iscarried out at relatively low temperature, preferably in the temperaturerange from 10 to 50° C., in particular from 10 to 30° C., andparticularly preferably at room temperature.

In order to minimize the reaction times, a photopolymerization ispreferably employed; in this case, any desired light sources, inparticular UV light-emitting sources, can be used (for example mercuryvapour lamps, xenon lamps or laser light).

One or more further layers are applied to the resultant organicallycrosslinked layer in the manner described until the desired multilayersystem is obtained. In the case of the final (outermost) layer, aseparate crosslinking step is no longer necessary, but instead this cantake place directly in the subsequent sealing and baking step f).

In step f), the multilayered system is heated at temperatures of from400 to 800° C., preferably from 400 to 600° C. and in particular from400 to 500° C., and held at this temperature for, for example, from 1minute to 1 hour. Complete removal of the organic (carbon-containing)constituents is carried out in this way without cracking or otherdefects occurring.

For this purpose, it is preferred to carry out the densification andbaking in step f) in such a way that the multilayered system is heatedfrom the outside inward in the direction of the substrate. This makes itpossible for the organic constituents present in the interior of thesystem to escape through the pre-heated outer layers. For the samereason, the layers are preferably heated at a heating rate of at least100 K/min.

The multilayered optical systems produced in accordance with theinvention are suitable, for example, as interference and anti-reflectionsystems for the following applications:

Optical filters: antireflection and reflection filters in the area ofthe spectacles industry, displays, display screens, semiconductorlasers, microlens coating, solar cells, damage-resistant laser layers,band pass filters, antireflection filters, absorption filters and beamsplitters.

Holographic layers: light deflection systems, information storage, lasercouplers, waveguides, decoration and architecture.

Embossable layers: bloom systems, focusing in detector fields,illumination of flat-panel display screens, imaging in photocopiers,fibre optics (light introduction).

Lithography: production of micro-optical elements, such as waveguides,gratings, pinholes, diffraction gratings (dot gratings) and in the areaof display technology, fibre-chip coupling and imaging optics.

The examples below serve for further explanation of the invention and donot have a restricting character.

Preparation of Coating Sols

EXAMPLE 1

Synthesis of a Sol for the Production of Layers of High Refractive Index

100 g of isopropanol are mixed with 18 g of methacrylic acid and 1.348 gof bidistilled H₂O. After the mixture has been stirred for 10 minutes,13.813 g of tetraisopropyl orthotitanate are slowly added dropwise withstirring. After the mixture has been stirred for 15 minutes, 10 g of2-isopropoxyethanol are added. The mixture is subsequently stirred at25° C. for 24 hours. A transparent, agglomerate-free sol ofsurface-modified TiO₂ nanoparticles is obtained.

0.08 g of 1-hydroxycyclohexyl phenyl ketone (IRGACURE 184, Ciba-Geigy)and 0.02 g of 1-methylimidazole are added to the sol; after vigorousstirring, the mixture is filtered and can then be employed as coatingmaterial.

EXAMPLE 2

Synthesis of a Sol for the Production of Layers of Low Refractive Index

31.388 g of TEOS are mixed with 20.264 g of ethanol. In parallel, 20.264g of ethanol, 0.9 ml of 4 M HCl and 22.275 g of bidistilled H₂O aremixed. The two mixtures are then combined. The TEOS sol can be employedafter about 10 minutes. 12.1 g of methacrylic acid are added withstirring. The reaction mixture is then stirred at 25° C. for 2 hours. Atransparent, agglomerate-free sol of surface-modified SiO₂ nanoparticlesis obtained.

The two sols are mixed in accordance with the desired solids content ofSiO₂ or TiO₂, the dilution being set using isopropanol. In addition,0.45% of the total weight of flow-control agent (BYK®-306,polyether-modified polydimethylsiloxane solution) is added to themixture. 0.08 g of 1-hydroxycyclohexyl phenyl ketone (IRGACURE® 184,Ciba-Geigy) and 0.02 g of 1-methylimidazole are added to the sol. Aftervigorous stirring, the mixture is filtered and can then be used ascoating material.

EXAMPLE 3

Synthesis of a Sol for the Production of Layers of High Refractive Index

0.663 g of tributyl phosphate are added to 28.95 g of TiO₂ sol, preparedas described in Example 1, and the mixture is stirred for 3 hours. Asolution of 0.4 g of distilled γ-glycidylpropyltrimethoxysilane (GPTS)in 30 g of 2-isopropoxyethanol is subsequently added dropwise to the solat 100° C. After 1 hour, the batch is cooled to room temperature, and0.3 g of hydrolysed GPTS is added. In order to carry out the GPTShydrolysis, 2.70 g of 0.1N HCl solution are added to 23.63 g of GPTS(dist.), and the mixture is stirred for 24 hours. Thelow-molecular-weight reaction products are subsequently removed bydistillation at 3 mbar, 25° C. After the mixture has been stirred for 15minutes, the batch is distilled under reduced pressure of 3 mbar andsubsequently diluted with 120 g of 2-isopropoxyethanol. A transparent,agglomerate-free sol is obtained.

EXAMPLE 4

Synthesis of a Sol for the Production of Layers of Low Refractive Index

0.96 g of 0.1N HCl solution is added to a mixture of 11.81 g of GPTS(dist.) and 4.15 g of tetraethoxysilane (TEOS) for hydrolysis andcondensation. The reaction mixture is then stirred at 20° C. for 24hours, after which the low-molecular-weight constituents are strippedoff at 3 mbar in a vacuum distillation. The reaction product whichremains is subsequently diluted with 22 g of isopropoxyethanol assolvent. 0.08 g of 1-hydroxycyclohexyl phenyl ketone (IRGACURE®184,Ciba-Geigy) and 0.02 g of 1-methylimidazole are then added to the sol.After vigorous stirring, the mixture is filtered and can them beemployed as coating material.

Production of Interference Layer Packages

EXAMPLE 5

Production of a 2-layer Antireflection Coating (Quarter-wave TiO₂ andQuarter-wave SiO₂) on Glass

A sheet of glass is cleaned and then coated with the sol from Example 1by dip coating (drawing rate 2.5 mm/s) and subsequently dried by meansof a UV drier (Belltron) at a belt speed of 2 m/min and a UV irradiationpower of 450 mW/cm². The sheet is subsequently dip-coated with the solfrom Example 2 at a drawing rate of 3.2 mm/s.

The double-coated sheet is then placed directly in an oven preheated at450° C. and left there for 10 minutes. Finally, the sheet is removedfrom the oven and cooled to room temperature in air. The sheet has ananti-reflection coating with the reflection spectrum shown in FIG. 1. AV-filter with a reflection minimum of 0% at a wavelength of 560 nm isevident.

EXAMPLE 6

Production of a 3-layer Antireflection Coating on Glass

The coating sol from Example 1 is mixed vigorously with the coating solfrom Example 2 in the ratio 1:0.7% by weight (solids). A sheet of glassis coated with this sol mixture by the dipping method at a drawing rateof 2.7 mm/s and cured with UV light analogously to Example 5. In orderto prepare the coating sol for the second layer, the sol from Example 1is mixed with the sol from Example 2 in the ratio 1:0.85% by weight(solids), and the sheet is then dip-coated at a drawing rate of 2.85mm/s and subsequently cured using UV light analogously to Example 5. Inthe next step, the sheet is dip-coated with the sol from Example 2 at adrawing rate of 3.6 mm/s.

The triple-coated sheet is then placed directly in an oven preheated to450° C. and left there for 10 minutes. Finally, the sheet is removedfrom the oven and cooled to room temperature in air. The sheet now hasan antireflection coating with the reflection spectrum shown in FIG. 2.It can be seen that the reflection spectrum after UV exposure has the Wfilter shape which is typical of a 3-layer structure. The one-stepbaking produces a reflection minimum throughout the spectral region from380 nm to 610 nm with a residual reflection of ≦2%. In the range between450 nm and 560 nm, the reflection is less than 1%, and 0% reflection isachieved at 500 nm. The measured curve agrees very well with the curvecalculated via simulation.

EXAMPLE 7

Production of a 5-layer Antireflection Coating

A sheet of glass is cleaned by the usual methods and dip-coated firstlywith the sol from Example 1 at a drawing rate of 1.2 mm/s andimmediately cured using UV (analogously to Example 5). The sheet is thendip-coated with the sol from Example 2 at a drawing rate of 2.45 mm/sand again cured by means of UV. The sheet is then dip-coated again withthe sol from Example 1 at a drawing rate of 1.2 mm/s and cured by meansof UV. The sheet is then dip-coated again with sol from Example 2 at adrawing rate of 2.45 mm/s. A coating with the sol from Example 1 is thenagain applied at a drawing rate of 1.2 mm/s.

The pentuple-coated sheet is then placed directly in an oven preheatedto 450° C. and left there for 10 minutes. Finally, the sheet is removedfrom the oven and cooled to room temperature in air. The sheetrepresents an interference filter with 5 individual layers on each sideand with the transmission spectrum shown in FIG. 3. A band pass filterfor the wavelength range between 620 nm and 900 nm is evident.

What is claimed is:
 1. A method for producing an inorganic multilayeredoptical system, comprising the steps of: (a) applying to a glasssubstrate a flowable composition comprising nanoscale inorganic solidparticles having polymerizable and/or polycondensable organic surfacegroups, the flowable composition being such that when polymerized and/orpolycondensed to form an organically crosslinked layer on the glasssubstrate and then baked to remove organic constituents and densify thelayer, it has a refractive index; (b) polymerizing and/or polycondensingthe organic surface groups of the solid particles, thereby forming theorganically crosslinked layer; (c) applying to the organicallycrosslinked layer a flowable composition comprising nanoscale inorganicsolid particles having polymerizable and/or polycondensable organicsurface groups, the flowable composition being such that whenpolymerized and/or polycondensed to form an organically crosslinkedlayer and then baked to remove organic constituents and densify thelayer, it has a refractive index that is different from the refractiveindex of the layer beneath; (d) polymerizing and/or polycondensing theorganic surface groups of the solid particles of the flowablecomposition of step (c), thereby forming the organically crosslinkedlayer; (e) optionally repeating steps (c) and (d) at least once, therebyforming at least one more organically crosslinked layer on the layersalready present; and (f) baking the multilayered substrate, therebyremoving organic constituents and densifying the layers to form theinorganic multilayered optical system.
 2. The method of claim 1 wherestep (d), or the last step (d) if step (e) is performed, is performed bybaking as a part of step(f).
 3. The method of claim 1 where the steps offorming the organically crosslinked layers are performed in thetemperature range from 10° C. to 50° C.
 4. The method of claim 3 wherethe steps of forming the organically crosslinked layers are performed inthe temperature range from 10° C. to 30° C.
 5. The method of claim 1where the steps of forming the organically crosslinked layers comprisephotochemically polymerizing and/or polycondensing the organic surfacegroups of the solid particles.
 6. The method of claim 1 where the stepof baking is performed at a temperature in the range from 400 to 800° C.7. The method of claim 6 where the step of baking is performed at atemperature in the range from 400 to 600° C.
 8. The method of claim 1where the step of baking is performed by heating the multilayeredsubstrate from an outermost organically crosslinked layer inward in thedirection of the substrate.
 9. The method of claim 8 where the heatingrate for the layers is at least 100 K/min.
 10. The method of claim 1where the nanoscale particles are nanoscale particles of metalcompounds.
 11. The method of claim 10 where the nanoscale particles areselected from nanoscale particles of metal oxides, metal sulfides, metalselenides, metal tellurides, and mixtures thereof.
 12. The method ofclaim 11 where the nanoscale particles are selected from nanoscaleparticles of SiO₂, TiO₂, ZrO₂, ZnO, Ta₂O₅, SnO₂, Al₂O₃, and mixturesthereof.
 13. The method of claim 1 where the polymerizable and/orpolycondensable surface groups are selected from organic radicalscontaining an acrylyl, methacrylyl, vinyl, allyl, or epoxide group. 14.The method of claim 1 where the solid particles have been produced bysurface modifying nanoscale inorganic solid particles with thepolymerizable and/or polycondensable surface groups.
 15. The method ofclaim 1 where the solid particles have been produced by a method usingat least one compound containing the polymerizable and/orpolycondensable surface groups.
 16. The method of claim 1 where thenanoscale inorganic solid particles have been produced by the sol-gelmethod.
 17. The method of claim 1 where each flowable composition has apH in the range from 3 to
 8. 18. An inorganic multilayered opticalsystem produced by the method of claim
 1. 19. An interference filter oranti-reflection system comprising the inorganic multilayered opticalsystem of claim 18.